Heretofore, many technical papers have been issued on magnetic alloys comprising rare earth elements and transition metals. Of the various alloys disclosed, an alloy comprising rare earth elements and cobalt has been considered particularly promising as permanent magnetic material. In fact, permanent magnets of the RCo.sub.5 type and of the R.sub.2 Co.sub.17 type are now in use.
However, as is well known in the art, it has experimentally been confirmed that intermetallic compounds and alloys of rare earth elements and Ni alone, or Fe alone, respectively, have no possiblity of being used as permanent magnetic material.
For example, E. A. Nesbitt et al "Journal of Applied Physics" Vol. 33, No. 5 May (1962) p. 1677 report on the temperature dependence of magnetic moment of intermetallic compounds and alloys of Ni and rare earth elements, such as SmNi.sub.5, PrNi.sub.5, YNi.sub.5 etc.. According to this report, even for the RNi.sub.5 type compound, which is crystal-structurally similar to the above mentioned RCo.sub.5 type compound, magnetic moment is substantially zero over all the usual service temperature range. This means that this type of material has no possibility of being used as permanent magnetic material.
S. C. Abrahams et al "J. Phys. Chem. Solids" Pergamon Press (1964) Vol. 25 p. 1077 show data on Curie point, which is one of important properties of permanent magnetic material, with respect to a certain number of rare earth-nickel intermetallic compounds. According to this report, LaNi.sub.5 and CeNi.sub.5, for examle, possess Curie point fo 1.4.degree. K. and SmNi.sub.5 25.degree. K. at highest, the latter showing the highest among the reported Curie points for RNi.sub.5. These temperatures are all below the ambient temperature. Thus, there is apparently no possibility that these materials may be used as permanent magnetic material at ambient temperatures.
K. Strnat et al "IEEE Trans. on Mag." Vol. MAG-2, No. 3, September 1966, pp. 489-493, under the title "Magnetic Properties of Rare Earth-Iron Intermetallic Compounds" report on physical properties essentially required as permanent magnetic material as to rare earth-iron alloys. It is, however, concluded that these alloys have no possibility of being used as permanent magnetic material, since the maximum Curie point for a series of alloys ranging from RFe.sub.7 to R.sub.2 Fe.sub.17 is 187.degree. C. (that of Gd.sub.2 Fe.sub.17).
Therefore, it has experimentally been affirmed hitherto in the prior art that alloys of rare earth elements with nickel or iron alone, respectively, cannot be used as permanent magnetic material.
Furthermore, there have been issued a number of patents on permanent magnetic alloys of rare earth elements and transition metals. For example, U.S. Pat. Nos. 3,421,889; 3,839,102; 3,947,295; 3,950,194; 3,982,971; 4,047,982; 4,081,297; 4,082,582; 4,099,995; 4,116,726; 4,121,952; 4,131,495; and 4,135,953. However, none of them have proposed the incorporation of nickel in these alloy systems. U.S. Pat. No. 3,560,200 (E. A. Nesbitt et al) discloses and claims RE-Co (and/or Fe)-Cu alloys and suggests that Cu may be partially or totally substituted with nickel or aluminium. However, it also states that it is clearly desirable to utilize as little as possible of copper, nickel and of aluminium, since it makes little magnetic contribution to the final composition at usual operating temperatures.
Thus, the prior art does not disclose and/or recognize anything about magnetic properties which will be obtained by incorporating both Ni and Fe in the rare earth-containing alloy system.
While we have found that particular compositions containing rare earth and (Fe+Ni) show excellent magnetic properties and other useful commercial properties, these alloys per se are not permanent magnetic in absence of addition of binder.